AN AIR CARRIER PILOT REPORTS DIFFICULTY DETERMINING THAT THE END OF GEG TAXIWAY 'A' TURNS RIGHT 90 DEGS BEFORE A NOT-WELL-DEFINED AND ABANDONED NO-TAXI RUN-UP AREA.

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I HAVE BEEN THROUGH GEG THREE TIMES IN THE LAST THREE WEEKS; ALL THREE TIMES WE HAVE DEPARTED RWY 21. AS YOU TAXI NE ON ALPHA TO RWY 21; THE TAXIWAY MAKES A 90 DEGREE TURN TO THE RUNWAY. STRAIGHT AHEAD (IF YOU WERE NOT TO MAKE THE TURN) IS WHAT LOOKS LIKE AN OLD BLACKTOP RUN UP AREA. THE FACT THAT THIS IS NOT AVAILABLE FOR AIRCRAFT MOVEMENT ANYMORE IS VERY POORLY MARKED AND IT LOOKS LIKE AN INVITING PLACE TO TAXI AN AIRPLANE. I WAS THERE UNDER THREE DIFFERENT WX CONDITIONS. THE FIRST DAY IT WAS VFR WITH RAIN. WITH THE CLOUDY CONDITIONS AND WET PAVEMENT; IT WAS VERY HARD TO SEE THE TAXIWAY EDGE PAINT. I IMMEDIATELY NOTICED THIS AS A POTENTIAL PITFALL BECAUSE I HAD MENTALLY NOTED THE TAXI ROUTE ON MY ARPT DIAGRAM AND DIDN'T RECALL SEEING A RUN UP PAD ON THE DIAGRAM. FURTHERMORE I DIDN'T SEE ANY TAXIWAY LIGHTS UNTIL AFTER THE 90 DEGREE TURN. THE NEXT WEEK IT WAS IFR IN RAIN SO THE TAXIWAY LIGHTS WERE ON. I HAD ALERTED THE CAPTAIN TO THIS POTENTIAL PROBLEM AND WHEN HE FINALLY SAW WHAT I WAS TALKING ABOUT AND SAW HOW EASY IT WOULD BE TO TAXI STRAIGHT OFF THE TAXIWAY; HE REACTED WITH EXPLETIVES. THE GOOD THING I NOTICED ON THIS DAY IS THAT THERE ARE TAXIWAY LIGHTS THERE. THEY ARE JUST IN PAVEMENT; WHICH EXPLAINS WHY I COULDN'T SEE THEM ON MY PREVIOUS VISIT. THE LAST TIME I WAS THERE; IT WAS A CLEAR DAY AND WITH THE DRY PAVEMENT; YOU COULD SEE THE TAXIWAY EDGE LINES QUITE CLEARLY. MY CONCERN IS A SNOW DAY WHERE THE IN PAVEMENT LIGHTS AND MARKINGS ARE OBSCURED; OR A WET DAY LIKE THE FIRST DAY I WAS THERE WHEN THE LIGHTS WERE NOT ON. IT IS MY OPINION THAT IT IS A MATTER OF TIME BEFORE SOMEONE TAXIES INTO THIS AREA. THERE NEEDS TO BE AN ELEVATED SIGN OR MARKING OF SOME SORT TO ALERT PILOTS NOT TO GO INTO THAT AREA.